3.3 Plant Disease: Biology Practice Questions AQA GCSE

Methods to avoid herbivory are widespread in many different species of plants. Whilst these adaptations help to protect plant tissues from damage, they also protect from the entry of pathogens. Suggest why does a defence against herbivores also defend against pathogens?

A defence against herbivores defends against pathogens as well because: Herbivores leave openings in the plant's defences to allow pathogens to enter OR damage to tissues provides an entry point / break in the physical barriers where pathogens can enter.

A farmer identified that a number of his plants were showing signs of disease. The farmer researched the symptoms of one of his plants and the research suggested that a possible cause of the symptoms was a magnesium deficiency. Magnesium deficiency symptoms include: Yellow leaves Stunted growth Explain how a deficiency of magnesium could cause these symptoms.

A deficiency of magnesium could cause the symptoms because: Yellow leaves due to lack of chlorophyll (not ‘chloroplasts’); (therefore) less / no light absorbed (by chlorophyll); (therefore) lower rate of / no photosynthesis; (therefore) plant makes less / no sugar / glucose; (therefore) plant converts less / no sugar / glucose into protein (for growth, so growth is stunted).

A common plant disease is caused by the tobacco mosaic virus (TMV). Describe how a gardener would be able to recognise that their plants were infected with TMV.

A gardener would be able to recognise that their plants were infected with TMV by observing a 'mosaic' pattern of discolouration on the leaves.

Which of the following options is not a method used to detect disease in plants? A. Variegated leaves B. Spots on leaves C. The presence of pests D. Tumour growth

A. Variegated leaves

Another strategy that the farmer could use would be to take cuttings from resistant plants and clone them. Evaluate whether cloning is a better strategy for the farmer to use to get resistant crops than selective breeding.

An evaluation of cloning vs selective breeding is: Both methods prevent the plants from dying from that disease; Cloning is quicker / selective breeding takes a long time/several generations; With cloning all the plants are genetically identical / selective breeding has more genetic variation; Cloned plants may be susceptible to other diseases / variation in selectively bred plants means that is less likely.

The student made the following conclusion: "The higherthe nitrate concentration in soil,the taller plants will grow." Using evidence from Table 1 and your own knowledge, evaluate this student's conclusion.

An evaluation of the student's conclusion is: In support of the conclusion: A maximum of three from the following: The data in Table 1 shows that the mean height of the plant increases with nitrate concentration; Nitrates are needed to make amino acids; Amino acids are used for protein synthesis; Protein synthesis is needed to help the plant to grow; Against the conclusion: A maximum of three from the following: Need to test a wider range of nitrate levels; Need to repeat with more plants at each nitrate level; Experiment only used one species of plant/broad bean plants / need to repeat with more species; There could have been other factors influencing the growth of the plants eg. light levels or disease.

A gardener is growing tomatoes in their garden. They have identified that the tomato plants have been infested with a large number of aphids which are reducing the growth of the tomatoes. The gardener would like to remove the aphids and is considering two different options for treatment: Option 1: Chemical pesticides, which are poisons that the gardener can spray in the garden which will kill all insects. Option 2:Biological control, which involves releasing large numbers of ladybirds into the garden Evaluate the use of chemical pesticides and biological control in the garden to remove the aphids.

An evaluation of the two options is as follows: Any four from: Both would successfully lead to the death of the aphids; Chemical pesticides risk harming other insects in the garden / not specific to the pest species / biological control is specific; Biological control can last for several generations / don't need to be reapplied / chemical pesticides need to be reapplied frequently / can wash away in the rain; Biological control could move away / could choose to eat something else / insects are unpredictable; Biological control might not eat all the aphids / chemical pesticides will kill all the pests; Chemical pesticides could lead to bioaccumulation / could pass along the food chain and harm other species.

One of the places that caffeine is stored in the plant cell is the vacuole. The vacuole is useful for storage, but it also has another important role in the plant cell. What is the other important role of the vacuole in the plant cell? A. To carry out protein synthesis B. To support the plant cells by making them turgid C. It contains chlorophyll to carry out photosynthesis D. To produce energy for the cell through the process of respiration

B. To support the plant cells by making them turgid

A gardener notices that the leaves of one of his rose plants are covered in black and purple spots. Name the disease affecting the gardener's rose plant.

Black spot disease / black spot / rose black spot disease.

One of the symptoms listed in Figure 1 is chlorosis. What is chlorosis?

Chlorosis is yellowing of the leaves of a plant (due to a lack of chlorophyll).

Another place that caffeine can be found is in the soil surrounding the coffee plant. When found in the soil, caffeine prevents seeds from germinating in that region. Why does this benefit the plant?

Having caffeine in the soil is beneficial because: It reduces competition with other plants; Plant has more access to resources/named resource e.g. light, water, minerals, space.

Coffee plants produce a poisonous chemical called caffeine that acts as a pesticide, meaning that it kills insects that eat the plant. The highest concentration of caffeine can be found in growing coffee seedlings. Suggest why this stage of the plant lifecycle benefits from having such a high concentration of caffeine.

Having the highest concentration of caffeine in the seedlings benefits the plant because: Any two from: The plant is most vulnerable to herbivores when it is a seedling; It has not yet developed its protective features e.g. bark; To increase the opportunity to grow into an adult plant OWTTE.

Figure 3 shows the arrangement of rose plants in the gardener's garden. The infected plant is labelled I. The gardener decides to move the plants labelled A and B to the other side of the garden (the area labelled X)to try and prevent the infection from spreading. He decides not to use a fungicide. Evaluate the effectiveness of the gardener's decisions in controlling the spread of the infection amongst the plants.

In support of his decisions: At least one of the following: The fungus that causes black spot is spread by wind (and water); They would be vulnerable to infection / fungus is likely to spread to them if they were left in their original locations; Against his decisions: Up to three of the following: Fungicides may damage other fungal cells / could be harmful to other organisms; If the wind direction changes, A and B would be at risk of infection; Using a fungicide would give additional protection / isn't dependent on wind direction.

The black streaks on the leaves of plants infected by Black Sigatoka, appear as a result of the cells inside the leaf being digested by enzymes from the pathogen. The fungi release the enzymes extracellularly (outside of their cells) and then absorb the nutrients from the digested plant cells. Why is it possible for fungito digest their food extracellularly instead of having an internal digestive system?

It is possible for fungi to digest their food extracellularly because: They have a large surface area : volume ratio; They can rely on diffusion directly into their cells.

Suggest why it is not always the best option for growers to increase the amount of nitrate in the soil if their plants aren't growing as tall as expected.

It might not always be the best option to increase the amount of nitrate in the soil because: Any two from: Plants can only absorb nitrates at a certain rate / too much nitrate can lead to pollution/damage to the environment; Not all stunted growth is caused by a nitrate deficiency / the plant may be diseased or suffering from a different mineral deficiency; It may not be cost effective / extra money spent on nitrate might not be equivalent to the extra money made from the increased yield.

List some methods that can be taken by people that own banana plantations in order to prevent the spread of Black Sigatoka amongst their plants. Name three methods.

Methods to prevent the spread of Black Sigatoka include: Any three from: Reducing spread by water by having good drainage of fields / reducing irrigation around infected plants; Burning infected plant material; Treating infected plants with antifungal treatments; Disinfecting clothing / tools that come into contact with infected plants.

Suggest how monoclonal antibodies could be used to confirm that TMV was the cause of the disease in the gardener's plants.

Monoclonal antibodies could be used to confirm that TMV was the cause of the disease in the gardener's plants by... Any three of the following: Monoclonal antibodies (mAbs) are complementary/specific to the TMV antigen; Antibodies are bound to a fluorescent dye; Antibody-antigen complex could result in antibody-dye sticking to the plant/test material / being observed; Enzyme catalyses a reaction which causes an observable result.

Minerals enter the plants through the roots. Describe the process that allows plants to absorb mineral ions into their roots.

Plants absorb mineral ions into their roots by: Any three from: Active transport; into root hair cells; Mineral ions move from where they are in low concentration in the soil, to high concentration in the root (hair cells) / movement is against the concentration gradient; This process requires energy.

This question is about how plants defend themselves against pathogens. Complete the sentences by picking one of the words in bold in each set of [ ] brackets. 1. Plant cells have physical barriers to defend themselves against the entry of pathogens. An example is the cell wall made of [starch / chitin / cellulose] that acts as a barrier. 2. A physical barrier around the outside of the leaf is called the [waxy cuticle / guard cells / palisade mesophyll]. 3. The outside of trees have a thick protective layer of dead cells around the stems called [cork / xylem / bark].

Plants defend themselves from pathogens by: Plant cells have physical barriers to defend themselves against the entry of pathogens. An example is the cell wall made of cellulose that acts as a barrier; A physical barrier around the outside of the leaf is called the waxy cuticle; The outside of trees have a thick protective layer of dead cells around the stems called bark.

Plants can be infected by a range of pathogens. Aphids are small insects that feed on plant sugars and carry pathogens. Figure 1 shows an aphid feeding on a plant. Plants infested with aphids show signs of reduced growth. Suggest and explain one reason why.

Plants infested with aphids show signs of reduced growth because... Any one of the following pairs of answers: Less food / sugars available (to the plant) for respiration; Less energy released to the plant; OR Fewer amino acids made (linked to reduction in sugars); So less protein made / less protein synthesis for growth; OR Less cellulose made; So cell walls are weaker.

TMV can cause plants to produce less chlorophyll. Explain why plants with TMV exhibit stunted growth.

Plants with TMV exhibit stunted growth because: Less chlorophyll would result in less photosynthesis / the plant absorbs less light Less sugar/glucose is made/synthesised therefore Less respiration means less energy is generated for growth Because glucose is needed for respiration and/or Less amino acids/proteins / cellulose available for growth (as building materials) Because glucose is needed to make these materials

The passion flower (Passiora) is a genus of plant that produces leaves with small yellow spots, as shown in Figure 3. The spots on the leaves have evolved to mimic the eggs of butterflies. What category of adaptation does this feature fall into? Pick one option: Physical Mechanical Chemical

The adaptation is mechanical.

Black Sigatoka is a type of plant disease caused by the fungal pathogen Mycosphaerella fijiensis. It mainly infects banana plants and one of the main symptoms is that the leaves appear to have black streaks across them. The fungal spores spread in the wind and in water droplets from plant to plant. They enter via the leaves. Using Figure 1,identify the area of the leaf that allows the entry of pathogens

The area of the plant the allows pathogens to enter is the stoma.

Describe the cause of this disease and explain how the plant is affected by it.

The cause of the disease is... A fungus / fungal pathogen; The effects of the disease are... The black spots reduce the amount of light that can be absorbed / block chlorophyll from receiving light; So less photosynthesis occurs; This reduces plant growth (because there is less sugar available).

Plants require certain minerals in order to grow. If the plant does not get enough minerals it can exhibit symptoms of a deficiency, such as those listed below in Figure 1. Draw one line from each type of mineral in Figure 1 to the symptom the plant shows when it is deficient in that mineral.

The correct symptom for each mineral deficiency is:

If a crop plant growing in a farmer's field experiences a mineral deficiency it might have a reduced yield. This would result in the farmer losing money when they go to sell their crops after harvest. What could the farmer do to their fields to prevent their plants experiencing a mineral deficiency?

The farmer could reduce the risk of mineral deficiency by spreading fertilisers /manure on the fields.

After the farmer lost a large number of his plants to disease they decided to try breeding some resistant strains on the farm. The farmer will selectively breed some of the surviving plants in order to achieve this. Describe how the farmer would do this.

The farmer would selectively breed the plants by: Selecting two of the surviving plants that are resistant to the disease; Breed them together; Select the offspring that are also resistant to disease; Repeat this process for several generations.

Other minerals are essential for optimum plant growth. NPK fertilisers are three-part fertilisers containing nitrogen (N), phosphate (P) and potassium (K) in varying proportions. Plants deficient in potassium have stunted roots. Plants deficient in phosphate ions cannot form flowers and fruits. The percentages (%) of minerals in three commercially-available NPK fertilisers were compared. The gardener used this data to decide which fertiliser to buy. The data are shown in Table 1. The gardener decided to buy Fertiliser 2. Explain why he chose Fertiliser 2.

The gardener chose Fertiliser 2 because... Any four of the following: 2 has the same % nitrogen (for good growth) as 1; 2 has the highest potassium content for root development; 2 is double the price of 3, but contains more than 4× the % of each mineral; However, a trade-off is that 2 has much less phosphate than 1; 1 is 3× the price of 2 and possibly contains excess/unneeded phosphate; Flowers/fruit perhaps less important for the gardener / minerals for growth and root development more important to the gardener.

As well as causing reduced growth, aphids can also act as vectors for disease. The gardener notices that some of his plants have a slight yellowing of some of the leaves after being infested with aphids. How could the gardener find out what disease the tomato plants are infected with?

The gardener could find out by: Any two from: Using a gardening manual or website; Taking infected plants to a laboratory to identify the pathogen; Using testing kits that contain monoclonal antibodies.

Suggest why the gardener washes all of their tools in disinfectant after using them on TMV-infected plants.

The gardener washes all of their tools in disinfectant after using them on TMV-infected plants because: to destroy the virus / stop it from spreading.

Newly-hatched aphids do not have wings. After a number of generations, a number of aphids hatch with wings. A mutation in one population of aphids results in the wings failing to develop. Suggest the impact of this on the aphid and other organisms

The impact of aphids' wings failing to develop could be... Any two of the following: Aphids cannot fly to colonise other plants / another part of the same plant; (So) there is increased competition for food; Aphids cannot escape predators.

The results of the investigation are shown in Table 1. Using Table 1, calculate the mean height of the plants in the high soil nitrate concentration after two weeks.

The mean height of the seedlings was: (34 + 32) ÷ 2; = 33.

Using Figure 2, describe what would happen to the number of aphids if a disease caused the number of ladybirds to decrease.

The number of aphids would increase because they are not being eaten by the ladybirds.

A farmer surveyed their plants for symptoms of TMV. During the survey the farmer identified that 24 of his 359 plants showed signs of having the disease. What percentage of his crop had symptoms of TMV?

The percentage of crop that had symptoms of TMV was: (24 ÷ 359) x 100; = 6.7%.

When plants are infected with Black Sigatoka they have stunted growth and 50% lower fruit yield. Explain why this occurs.

The plants have stunted growth and 50% lower fruit yield because: Any two from: Damage to leaf tissue / black patches on the leaves means fewer chloroplasts; Plants have reduced photosynthesis; They produce less glucose / starch / biomass

Plants have methods of protecting themselves from attack. One such method is the production of oils by cells on the surface of leaves. Suggest how the production of oil might protect a plant from being attacked.

The production of oil might protect a plant from being attacked by... Any one of the following: Insects slide/slip off because the oil makes the leaf difficult to land on; Insects feed on the oil which is unpleasant; The oil is harmful to / kills insects; The oil has antibacterial properties / kills bacterial pathogens; The oil prevents ingress of / blocks water which could be carrying bacterial pathogens.

Scientists working for a skincare company investigated how effective three different plant oils were at preventing the growth of one strain of E. coli bacteria. Figure 4 shows their results. Evaluate the effectiveness of the three plant oils.

The results can be evaluated as follows: Any four from the following: The most effective oil was tea tree oil / tea tree oil produced the largest zone of inhibition; The least effective oil was rose oil / rose oil produced the smallest zone of inhibition; The control showed no inhibition of growth / confident that the oils were inhibiting growth; The skincare company should use tea tree oil; Only one study / experiment should be repeated to confirm findings / conduct further tests on different concentrations of tea tree oil / on different species of bacteria.

The farmer also thinks their strawberry crop is infected with a fungal pathogen Botrytis cinerea. The farmer obtains a monoclonal antibody test kit for Botrytis cinerea. To make the monoclonal antibodies a scientist first isolates the Botrytis cinerea protein from the fungi. Describe how the scientist would use the protein to produce the Botrytis cinerea monoclonal antibody.

The scientist would use the protein to produce the antibodies by: Inject the protein / it into a mouse; Combine lymphocytes with tumour / cancer cells to make hybridoma (cells); Find a hybridoma which makes a monoclonal antibody specific to Botrytis cinerea; (The scientist) clones (the hybridoma) to produce many cells (to make the antibody).

It is common for plants infested with aphids to show signs of magnesium deficiency. Describe and explain the symptoms displayed by a plant with a magnesium deficiency.

The symptoms displayed by a plant with a magnesium deficiency are... Any two from the following: Yellow leaves; The plant makes less glucose; The plant's growth is stunted; The explanations of the above symptoms are... Any two from the following: (Yellow leaves) because the plant hasn't got enough magnesium to make enough chlorophyll; (Makes less glucose) because photosynthesis proceeds at a lower rate; (Stunted growth) because less glucose is available to be converted into protein; Less glucose is available to make cellulose for cell walls; Less energy is released for making proteins / other biomass.

Describe the symptoms the plant will show if it is infected with Tobacco Mosaic Virus (TMV).

The symptoms of tobacco mosaic virus are: Mosaic pattern of discolouration on leaves; Stunted growth

Figure 2 shows a food chain. What is the trophic level of the aphid in Figure 2?

The trophic level of the aphids is second trophic level / primary consumers.

Suggest why having a mimicry of butterfly eggs on the leaves might benefit the plant.

This might benefit the plant because: Any two from: Real butterflies think that the eggs belong to other butterflies; They do not lay their eggs on the leaves; to avoid competition with other caterpillars; This protects the plant from herbivory / being eaten by caterpillars.

Once the diseased plants have been identified, they then need to be treated. TMV has no cure. What can the farmer do to prevent the spread of the pathogen to other plants?

To prevent the spread of TMV the farmer can: Any one from: Burn the infected plant material; Sterilise gloves/clothing and any equipment used on the infected plants.

A number of mineral ions are needed by plants. Plants that are deficient in mineral ions will not be healthy. Name two essential mineral ions and describe the appearance of plants with deficiencies in these ions.

Two essential mineral ions and the appearance of plants with deficiencies in these ions are... Nitrate - deficiency leads to stunted growth; Magnesium - deficiency leads to yellowing of the leaves/chlorosis.

Many plants have varied strategies to avoid being eaten by herbivores, such as insects and animals. One adaptation is to produce poisonous chemicals. Name two other adaptations that plants can possess to defend themselves against herbivores.

Two other adaptations that plants can possess are: Any two from: Thick cellulose cell walls; Tough waxy cuticle; Bark / thick layers of cells around stems; Thorns; Hairs; Mimicry; Drooping leaves.

A number of plants in a garden are infected with a pathogen. Give two ways of identifying the pathogen that is infecting the plants in the garden.

Two ways of identifying the pathogen that is infecting the plants in the garden are... Any two of the following: Compare them to pictures in a gardening manual / website / plant identification app; Send to a laboratory for testing; Use testing kits that contain monoclonal antibodies/mAbs.

A student is planning an experiment to investigate the effect of mineral deficiency on the growth of plants. This is the method used. 1. Nine broad bean plants were grown for two weeks from seeds. 2. Each of the nine plants were grown in different types of soil, three in soil high in nitrates, three in medium levels of nitrate, and three in low levels of nitrate. 3. After the two week growth time the height of each of the plants was measured using a rule. Suggest two ways the student could improve their experiment.

Two ways the student could improve their experiment is: Any two from: Repeat the experiment with more plants per soil type; Control variables eg. water availability, light intensity, concentration of other minerals such as magnesium etc.; Use more specific quantities of nitrate rather than low/medium/high; Repeat with different plant species.

Witch hazel is a plant that produces oil as part of its defence against pathogens. Many skincare companies extract the oil to use in consumer products. The oil prevents bacteria from attacking the plant but is safe to use in skincare products. Suggest and explain a reason why.

Witch hazel oil is safe to use in skincare products because... The oil has antibacterial properties / works like an antibiotic; So it will affect the bacterial cells but not affect the skin / animal cells; It must target a process / structural feature of bacterial cells / not present in animals cells.